Tubular halogen cycle incandescent lamp with inner cylinder for universal operation



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D. H. GREEN 3,435,272 TUBULAR HALOGEN CYCLE INCANDESCENT LAMP WITH INNERCYLINDER FOR UNIVERSAL OPERATION Filed July 15, 1966 UPPEEEND a 2 aINTERN/9L LENGTH, [NC/1'55 ITWVEETWTOT'I David HGT-sen y am .f"

His Adv-kc neg United States Patent US. Cl. 313-222 5 Claims ABSTRACT OFTHE DISCLOSURE In an elongated tubular incandescent lamp of the halogencycle type, with an axial filament and containing an inert fill gas anda halogen getter, thermal separation of the halogen and the fill gas invertical operation of the lamp, is effectively minimized by atransparent cylinder concentrically arranged between the filament andthe lamp envelope.

This invention relates generally to electric incandescent lamps, andmore particularly to incandescent lamps of the halogen cycle typecomprising an elongated tubular envelope containing an axially extendingtungsten filament and a filling of inert gas together with halogen gasor vapor which functions as a regenerative getter to return to thefilament tungsten vapor evolved therefrom during operation of the lampto thereby prevent deposition of the tungsten vapor on the envelope wallas a dark coating. Such lamps, in which the halogen is iodine, are morefully disclosed and claimed in Patent 2,883,571 to Fridrich and Wiley.

Although such lamps have come into use with eminently successfulresults, when they are operated in positions inclined from thehorizontal the iodine and inert gas separate, with the iodine tending togo to the bottom of the lamp. In some cases there is not enough iodineat the top of the lamp to prevent tungsten blackening. This problem isparticularly acute in lamps having desirable internal diameters of lessthan about 20 mm. and greater than about 4 mm. and a length greater thanabout three times the diameter wherein there is a laminar flow of theinert gas upwardly along the filament and downwardly along the envelopewall. The phenomenon apparently occurs because the lamp when burnedvertically, or inclined as little as about 4 from the horizontal, actsas a thermal separation column. The iodine tends to diffuse radiallytoward the envelope wall and the convective motion of the inert fill gastends to pump it toward the bottom.

It is therefore an object of the present invention to provide a novelconstruction which will permit operation of the lamp in any position,including the vertical, by making the distribution of halogen moreuniform along the length of the lamp. It is a further object to achievethat result without the need for excessive amounts of halogen which tendto minimize the difficulty by simply providing more halogen throughoutthe envelope, but which can absorb a significant amount of light or, insome cases, attack portions of the filament and support members.

In accordance with the invention the halogen separation is effectivelydecreased by providing a light-pervious cylinder or sleeveconcentrically disposed in the lamp envelope between the upward anddownward path of the gas flow. The cylinder efiectively blocks one ofthe mechanisms of the separation phenomenon. Convective fiow of the fillgas still occurs with the gas moving upwardly within the inner cylinderand downwardly in the annular space between the cylinder and the innerenvelope wall. However, the difiusion of the halogen radially toward thePatented Mar. 25, 1969 envelope wall is blocked by the inner cylinder,thereby preventing the downward moving stream of fill gas from carryingthe halogen to the bottom of the envelope.

Further features and advantages of the invention will appear from thefollowing detailed description and from the drawing wherein:

FIG. 1 is a side elevation, in section, of a lamp comprising theinvention;

FIG. 2 is a schematic pictorial view of the lamp illustrating theconvective flow of the fill gas;

FIG. 3 is a chart showing an experimental determination of thedistribution of halogen over the length of a lamp containing iodine asthe halogen; and

FIG. 4 is a cross section of the lamp.

Referring to FIG. 1 of the drawing, the lamp illustrated thereincomprises a tubular envelope 1, preferably of essentially fused silicaor quartz, having therein an axially extending filament 2 of helicallycoiled tungsten wire. The filament is connected at respective ends, inthis case, by straightened end or leg portions 3 of the filament wire,to extremely thin strips of foil 4, preferably of molybdenum, which arehermetically sealed in pinch seal portions 5 at respective ends of theenvelope, and which are, in turn, connected to outer lead wires 6 whichmay also be of molybdenum.

The envelope 1 also contains a filling of inert gas such as nitrogen,argon, krypton or xenon, or mixtures thereof, preferably at a pressureof at least several hundred torr (mm. Hg), and also a small quantity ofhalogen. The filling of gas and halogen may be introduced by way of anexhaust tube the residue of which is shown at 7. When the halogen isiodine, it is preferably introduced in elemental form along with a smallamount of oxygen which is usually added with the inert fill gas asdisclosed, for example, in Patent 3,160,454 to Zubler et a1. When -ahalogen other than iodine is used, it is preferably introduced as acompound containing hydrogen, such as hydrogen bromide, or a halogenderivative of hydrocarbons, such as methyl or methylene bromide.

In accordance with the invention, in the vertical operation of lampshaving tubular envelopes, especially those of internal diameters withina range greater than 4 millimeters and less than 20 millimeters,separation of the iodine or other halogen from the inert gas issignificantly prevented or minimized, and early bulb blackening isavoided, by placing within the envelope 1 a concentrically arranged,open ended, cylinder 8 which may also be of quartz and which preferablyextends along at least the full length of the coiled filament 2. Thecylinder or sleeve 8 is herein illustrated as being supported by a pairof short quartz rods or spuds 9 which are tacked or fused to theenvelope 1 and cylinder 8. When desired, the filament 2 is provided withconventional auxiliary tungsten wire spiral supports spaced along thelength of the filament and engageable with the inner wall of thecylinder 8.

As illustrated in FIG. 2, during operation of the lamp there is alaminar flow of the fill gas upwardly along the filament 2 within thecylinder 8 and downwardly along the envelope 1 and outside the cylinder8, as indicated by the arrows. However, diffusion of the halogenradially toward the wall of the envelope 1 and into the downward flow ofthe fill gas, is blocked by the cylinder 8 so that vertical separationof the halogen is effectively decreased and much more uniformlydistributed along the length of the lamp.

The cylinder 8 is correctly positioned when the annular cross sectionalarea A1 (FIG. 4) between the filament 2 and cylinder 8 is approximatelyequal to the annular cross sectional area A2 between the cylinder 8 andenvelope 1.

By way of example, a 500 watt, volt lamp as shown in FIG. 1 and havingan envelope 1 of inch nominal outside diameter (about 7.5 millimeterinside diameter) and an inner envelope length, between the seals 5, of 3inches, was provided with an inner cylinder 8 of about 5 mm. insidediameter and 5.5 mm. outside diameter. The lamp was filled with argon ata pressure of 1,760 torr, and a small amount (about 3 micromoles) ofiodine were added. The iodine had been doped with a trace of iodine-131which is a radioactive gamma ray emitter. Thus the iodine distributioncould be measured while the lamp was lighted by counting the gamma rays.

The iodine distribution during vertical operation of the lamp was foundto be quite uniform along the length of the cylinder 8 as shown in theFIG. 3 chart wherein the abscissa is internal lamp length, in inches,and the ordinate is iodine concentration in arbitrary units. The upperend of the lamp is to the right in FIGS. 1 and 3. The iodineconcentration of the improved lamp comprising the invention is shown bythe dotted line curve A, in comparison with the concentration in anotherwise similar standard lamp without the cylinder 8 as shown by thesolid line curve B. The standard lamp would tend to blacken at the topbecause of insutficient iodine. The concentration of the improved lampremains effectively uniform for all lamp orientations from vertical tohorizontal, so that the lamp is universally operable in any position.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A halogen cycle electric incandescent lamp comprising alight-pervious elongated tubular envelope containing a coiled tungstenwire filament extending axially of said envelope and a filling of inertgas and halogen wherein, in a position of the lamp inclined from thehorizontal, there is a laminar flow of the gas in opposing pathsupwardly along the filament and downwardly along the envelope walltogether with migration of the halogen radially toward the envelope wallto a position to be swept downward to the bottom of the envelope by thedownward flow of the gas, and means to block the radial migration of thehalogen comprising an open ended lightpervious imperforate cylinderconcentrically disposed in said envelope between the upward and downwardpaths of the gas flow and coextensive With the coiled filament andproviding a generally uniform distribution of the halogen along thelength of said cylinder irrespective of the inclination of the lampduring operation.

2. A halogen cycle electric incandescent lamp as in claim 1 wherein thehalogen is iodine.

3. A halogen cycle electric incandescent lamp as in claim 1 wherein thehalogen is iodine and the inert gas is argon.

4. A halogen cycle electric incandescent lamp as in claim 1 wherein thehalogen is bromine.

5. A halogen cycle electric incandescent lamp as in claim 1 wherein thehalogen is bromine and the inert gas is argon.

References Cited UNITED STATES PATENTS 2,211,597 8/1940 Dorgelo et al3l3222 X 2,530,990 11/1950 Peters. 2,883,571 4/1959 Fridrich et a1313222 X JAMES W. LAWRENCE, Primary Examiner.

DAVID OREILLY, Assistant Examiner.

U.S. Cl. X.R.

